The present invention relates to an apparatus for estimating a pneumatic tire pressure. Especially, the present invention is preferably applicable to the system which indirectly estimates the pneumatic pressure of a tire based on a wheel speed.
As a conventional technique, for example, the unexamined Japanese patent publication No. 9-104208 corresponding to the U.S. Pat. No. 5,753,809 discloses a pneumatic tire pressure estimating apparatus which detects a resonance frequency from vibrational information of a tire and obtains a pneumatic tire pressure based on the detected resonance frequency. According to this conventional apparatus, to enable the pneumatic tire pressure detection in a limited microcomputer resource, the resonance frequency is simply obtained by using model approximation or by using linear prediction of time series vibrational information. The pneumatic tire pressure is estimated based on the thus simply obtained resonance frequency.
However, the above-described conventional technique basically relies on approximation in detecting the resonance point. This is disadvantageous in such a case that the information other than the objective resonance frequency is contained in the vibrational information. The frequency to be detected tends to be drawn toward peripheral noise components. The resonance frequency cannot be detected correctly. This will increase dispersion in the detection of resonance point.
On the other hand, to remove the influence of peripheral noise components, it will be possible to use filters having high damping properties or filters having narrow bands. However, if required to enhance the damping property, the order of filters will be necessarily increased up to several tens. It will require a limited high-performance microcomputer or a DSP. The cost of system will increase. Accordingly, the practical order of filters is limited to two to four.
Meanwhile, there is a conventional method for securing a required damping property by using narrow-band filters while the order of filters remains the same. However, when the resonance frequency disagrees with the central frequency of the filters, the resonance information itself will be distorted due to the influence of the filters. Hence, it will be difficult to accurately detect the resonance frequency.
In view of the above-described problems of the prior art, the present invention has an object to accurately detect the frequency information considering the influence of noise components.
To accomplish the above and other related objects, the present invention provides a first estimating apparatus for estimating a pneumatic tire pressure comprising tire vibrational information detecting means (1) for detecting vibrational information of a tire, filtering means (S102xcx9cS105, S202xcx9cS204) for filtering desired frequency information based on the vibrational information detected by the tire vibrational information detecting means, resonance frequency detecting means (S106xcx9cS112, S205xcx9cS211) for detecting a resonance frequency based on the frequency information filtered by the filtering means, and pneumatic tire pressure estimating means (3) for estimating a pneumatic tire pressure based on the resonance frequency. The filtering means of the first estimating apparatus is constituted by a plurality of filters having filtering effects different from each other. And, the resonance frequency detecting means of the first estimating apparatus comprises means (S106xcx9cS110, S205xcx9cS209) for obtaining frequencies (f1xcx9cf4) corresponding to the resonance frequency based on respective frequency information passing through the plurality of filters, and determining means (S111, S210) for determining an optimum frequency having less influence of noise based on the obtained frequencies, thereby obtaining the resonance frequency based on the optimum frequency determined by the determining means.
In the description of summary of the invention, the reference numerals in parentheses attached to the described means show the correspondence to practical components or steps explained in later-described practical embodiments.
With this arrangement, the frequencies corresponding to the resonance frequency are obtained from the frequency information passing through a plurality of filters. Thus, it becomes possible to obtain frequencies having different influences of noise components. Hence, it becomes possible to detect accurate frequency information having less influence of noise based on the thus obtained frequencies having different influences of noise components.
According to the first estimating apparatus of the present invention, it is preferable, when a dispersion width of the obtained frequencies (f2xcx9cf4) is within a predetermined value, the determining means (S111) identifies a central value (f4) among the obtained frequencies as the optimum frequency having less influence of noise. Furthermore, it is preferable, when a dispersion width of the obtained frequencies (f2xcx9cf4) is within a predetermined value, the determining means identifies an average value of the obtained frequencies as the optimum frequency having less influence of noise.
On the other hand, it is preferable that the determining means (S210) corrects the obtained frequencies (f1xcx9cf3) and identifies a corrected value as the optimum frequency having less influence of noise. For example, it is preferable that the determining means performs the correction based on a deviation of the obtained frequencies.
Furthermore, it is preferable that the determining means performs the correction only when the dispersion width of the obtained frequencies is within a predetermined value.
Furthermore, to change the degree of influence of noise components, it is preferable that the plurality of filters have different bandwidths or damping properties. It is preferable that the plurality of filters have different passbands.
For example, it is preferable that the plurality of filters comprise a first filter passing a first resonance frequency band including a desired frequency component, a second filter passing a second resonance frequency band narrower than the first resonance frequency band, and a third filter passing a third resonance frequency band narrower than the second resonance frequency band.
In this case, it is preferable that the first filter for setting the first resonance frequency band is constituted by a first lowpass filter for filtering a frequency region higher than the first resonance frequency band and a first highpass filter for filtering a frequency region lower than the first resonance frequency band. The second filter for setting the second resonance frequency band is constituted by the first lowpass filter and a second highpass filter having a cutoff frequency higher than that of the first highpass filter. And, the third filter for setting the third resonance frequency band is constituted by the second highpass filter and a second lowpass filter having a cutoff frequency lower than that of the first lowpass filter.
Furthermore, it is preferable that the frequencies (f1xcx9cf4) corresponding to the resonance frequency can be obtained based on calculation result of the means (S106xcx9cS108, S205xcx9cS207) for calculating a product-sum of respective frequency information passing through the first to third resonance frequency bands.
The present invention provides a second estimating apparatus for estimating a pneumatic tire pressure comprising tire vibrational information detecting means (1) for detecting vibrational information of a tire, filtering means (S102xcx9cS105, S202xcx9cS204) for filtering desired frequency information based on the vibrational information detected by the tire vibrational information detecting means, resonance frequency detecting means (S106xcx9cS112, S205xcx9cS211) for detecting a resonance frequency based on the frequency information filtered by the filtering means, and pneumatic tire pressure estimating means (3) for estimating a pneumatic tire pressure based on the resonance frequency. The filtering means of the second estimating apparatus is constituted by a plurality of filters having filtering effects different from each other. The resonance frequency detecting means of the second estimating apparatus comprises means (S305xcx9cS307) for obtaining gains (G1xcx9cG3) based on respective frequency information passing through the plurality of filters, and determining means (S311) for determining an optimum frequency having less influence of noise based on the obtained gains, thereby obtaining the resonance frequency based on the optimum frequency determined by the determining means.
The gains obtained from the frequency information passing through the plurality of filters are different from each other depending on the degree of influence of noise components. Hence, it becomes possible to detect accurate frequency information having less influence of noise based on the thus obtained gains having different influences of noise components.
For example, it is preferable that the resonance frequency detecting means comprises the means (S308xcx9cS310) for obtaining frequencies based on respective frequency information passing through the plurality of filters, and the determining means (S311) corrects the obtained frequencies (f1xcx9cf3) based on the gains to determine the optimum frequency having less influence of noise. For example, it is preferable that the determining means performs the correction based on a ratio of the gains.
It is also preferable that the determining means performs the correction only when a ratio of the gains is within a predetermined range.
It is also preferable that the plurality of filters have different passbands.